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GC overhead (Re: GCC 3.3, GCC 3.4)
- From: Matt Austern <austern at apple dot com>
- To: Geoff Keating <geoffk at geoffk dot org>
- Cc: Devang Patel <dpatel at apple dot com>, gcc at gcc dot gnu dot org
- Date: Mon, 3 Feb 2003 14:41:12 -0800
- Subject: GC overhead (Re: GCC 3.3, GCC 3.4)
On Monday, February 3, 2003, at 02:30 PM, Geoff Keating wrote:
Matt Austern at Apple did similar experiment by using ggc placeholder.
(same interface as ggc, no collection, allocate memory using mmap in
chunks and
satisfy memory allocation requests from these chunks etc..).
He got around ~12% speedup for sample c++ source.
To be precise, Matt found that the speedup of using the ggc
placeholder was about equivalent to the speedup of using ggc-page but
disabling garbage collection. This contradicts the results that Tim
Josling got above.
Yes. That's why I haven't been pushing to have a mode in which
gc is entirely removed: my measurements suggest that the most
important way in which gc introduces overhead is the most obvious
one: the collection phase itself takes time.
(Insert usual disclaimers about a single measurement not necessarily
being representative, independent replication of results being
important, the possibility of subtle effects on overall design of
the compiler, etc.)
--Matt